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Ecotoxicological information

Ecotoxicological Summary

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Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
4.9 µg/L
Assessment factor:
2
Extrapolation method:
sensitivity distribution

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
5.5 µg/L
Assessment factor:
2
Extrapolation method:
sensitivity distribution

STP

Hazard assessment conclusion:
PNEC STP
PNEC value:
157 µg/L
Assessment factor:
10
Extrapolation method:
assessment factor

Sediment (freshwater)

Hazard assessment conclusion:
PNEC sediment (freshwater)
PNEC value:
273 mg/kg sediment dw
Assessment factor:
3
Extrapolation method:
sensitivity distribution

Sediment (marine water)

Hazard assessment conclusion:
PNEC sediment (marine water)
PNEC value:
257 mg/kg sediment dw
Assessment factor:
3
Extrapolation method:
sensitivity distribution

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
PNEC soil
PNEC value:
332 mg/kg soil dw
Assessment factor:
1
Extrapolation method:
sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
PNEC oral
PNEC value:
17.1 mg/kg food
Assessment factor:
6

Additional information

Read-across

Lead di(acetate) is an inorganic solid salt at room temperature and consists of lead cations and acetate anions. Based on the solubility of lead di(acetate) in water (443 g/L at 20°C, CRC handbook, 2008), a complete dissociation of lead di(acetate) resulting in lead and acetate ions may be assumed under environmental conditions. The respective dissociation is reversible, and the ratio of the salt /dissociated ions is dependent on the metal-ligand dissociation constant of the salt, the composition of the solution and its pH.

The metal-ligand complexation constant of lead di(acetate) of 1.93 ± 0.04 (Bunting & Thong, 1969) points to a relatively low strength of the monodentate bond between lead and acetate.Based on an analysis by Carbonaro& Di Toro (2007)of monodentate binding of lead to negatively-charged oxygen donor atoms, including carboxylic functional groups, monodentate ligands such as acetate anions are not expected to bind strongly with lead. Accordingly, protons out-compete lead ions for complexation of monodentate ligands given equal activities of free lead and hydrogen ions.The analysis by Carbonaro & Di Toro (2007) suggests that the following equation models monodentate binding to negatively-charged oxygen donor atoms of carboxylic functional groups:

log KML = αO * log KHL + βO; where

KML is the metal-ligand formation constant, KHL is the corresponding proton–ligand formation constant, and αO and βO are termed the Irving–Rossotti slope and intercept, respectively. Applying the equation and parameters derived by Carbonaro & Di Toro (2007) and the pKa of acetic acid of 4.75 results in:

log KML = 0.442 * 4.75 + 0.631

log KML = 2.73 (estimated lead- acetate formation constant).

Thus, it may reasonably be assumed that based on the lead-acetate formation constant, the respective behaviour of the dissociated lead cations and acetate anions in the environment determine the fate of lead di(acetate) upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning resulting in a different relative distribution in environmental compartments (water, air, sediment and soil) and determine subsequently its (eco)toxicological potential.

In the assessment of the environmental fate and toxicity of lead di(acetate), read-across to the assessment entities soluble lead substances and acetic acid / salts is applied since only the ions of lead and acetate are available in the environment and determine its environmental fate.Since lead cations and acetate anions behave differently in the environment, including processes such as stability, degradation, transport and distribution, a separate assessment of the environmental fate of each assessment entity is performed. Please refer to the data as submitted for each individual assessment entity.

To evaluate the environmental fate and toxicity of lead di(acetate), information on the assessment entities lead cations and acetate anions were considered. For a documentation and justification of that approach, please refer to the separate document attached to section 13, namely Read Across Assessment Report for lead di(acetate).

Conclusion on classification

Lead di(acetate) classification

Aquatic toxicity data are not avaialble for lead di(acetate). Read-across to the assessment entities soluble lead substances and acetic acid /salts is applied for the assessment of lead di(acetate) since the ions of lead di(acetate) determine its fate and toxicity in the environment. Reliable data are available for soluble lead substances and acetic acid, which indicate that the moiety of ecotoloxicological concern are lead cations. Data for acetic acid indicate very low toxic potential to aquatic organisms and readily biodegradation under environmental conditions. Thus, the toxicity of lead di(acetate) is driven by the lead cation since a hazard was not identified for the acetate anion. The aquatic hazard assessment is based on the most toxic moiety, i.e. lead cations, based on a maximum lead content of 63.7 %. Please refer to the section for the respective assessment entity.

 

Acute (short-term) toxicity: The lowest acute toxicity reference value of 20.5 μg soluble lead ion/L is recalculated for lead di(acetate) since it is very soluble (625 g/L in water) resulting in an acute environmental reference value of 32.2 µg PbAc/L. In accordance with Tables 4.1.0 (a) and 4.1.3, lead di(acetate) meets classification criteria of acute (short-term) aquatic hazard category 1 with an acute M-factor of 10.

 

Long-term toxicity: The lowest chronic toxicity reference value of 6.1 μg soluble lead ion/L is recalculated for lead di(acetate) since it is very soluble (625 g/L in water) resulting in a chronic environmental reference value of 9.6 µg PbAc/L. The concept of “biodegradability” was developed for organic substances and is not applicable to inorganic substances such as lead. Thus, the surrogate concept of “removal from the water column” was developed to assess if respective metal ions such as lead ions are upon addition rapidly removed from the water column or remain in the water column and are able to excert chronic toxic effects. Rapid removal (defined as >70% removal of dissolved metal ions in 28 days) is considered equivalent to “rapidly degradable”. The TICKET UWM model was successfully applied to demonstrate rapid degradation equivalent (rapid elimination from the water column) for the soluble Pb ion. Indeed 70 % elimination from the water column is already reached in 2 h’s while also the binding to sediments is assured (no net release) being it slower than the elimination rate in water. The REACH Registration file further concludes no bioaccumulation levels that could lead to a concern for classification.

 

Thus, removal of lead ions from the water column is rapid and its remobilization from the sediment is relatively insignificant (Rader, 2010). Thus, lead ions are considered equivalent to ‘rapidly degradable” regarding the classification of long-term aquatic effects. In accordance with Tables 4.1.0 (b) (ii) and 4.1.3, lead di(acetate) meets classification criteria of long-term aquatic hazard category 1 with a chronic M-factor of 1. Hence, classification as Aquatic acute 1 (H400), acute M-factor 10 and Aquatic chronic 1 (H410), chronic M-factor 1 is required for lead di(acetate) in accordance with Regulation (EC) No 1272/2008.